A polarizing plate is usually produced by applying, as protective films, films made of cellulose triacetate as a major component on both sides of a polarizer in which iodine or a dichromatic dye to be arranged on and stuck to a polyvinyl alcohol. The cellulose triacetate film has high optical isotropy (low retardation value) and is, therefore, preferably used in applications requiring optical isotropy. On the other hand, it is demanded that optical compensation sheets (phase difference films) for use in, for example, a liquid crystal display device, have optical anisotropy (high retardation value), on the contrary. Therefore, a synthetic polymer film, e.g. a polycarbonate film or polysulfone film, which has a high retardation value, is commonly used as the optical compensation sheet. Also, it is demanded of recent liquid crystal display devices to have a more severe display performance and these devices are therefore expected to be more suppressed in optical performance fluctuation as a result of environmental temperature and humidity.
On the other hand, a cyclic olefin-based film attracts attention as a film which is more reduced in hygroscopicity and moisture permeability and also has a reduced optical performance fluctuation as a result of environmental temperature and humidity, compared with the cellulose triacetate film. In addition, it is being developed as films for polarizing plates or liquid crystal displays. As such a cyclic olefin-based polymer, hydrides of ring-opening polymers and addition polymers as shown below are proposed.
(i) Hydrides of Polymers Obtained by Ring-Opening
Hydrides of copolymers obtained by ring-opening of tetracyclodecene-based compounds (see Japanese Patent No. 3050196).
(ii) Addition Polymers
                (ii-1) Copolymers of ethylene and a norbornene-based compound (see JP-A-61-292601 (“JP-A” means unexamined published Japanese patent application)).        (ii-2) Addition polymers of norbornene, and addition copolymers of norbornene and an alkyl-substituted norbornene (see, B. L. Goodall et al., MetCon 97, Jun. 4-5, 1997).        (ii-3) Addition polymers of a carboxylate of norbornene, and addition copolymers of an alkyl-substituted norbornene and a carboxylate of norbornene (Macromolecules, Vol. 29, 2755 (1996) and PCT International Publication WO2004/49011).        (ii-4) Addition copolymers of an alkyl-substituted norbornene and a polar group-substituted norbornene (see JP-A-2002-20435).        
However, the aforementioned hydrides of ring-opening polymers and addition polymers have the following problems.
The cyclic olefin-based polymers of the above (i) and (ii-1) each have a relatively lower glass transition temperature, and it is therefore difficult to obtain cyclic olefin-based polymers having high glass transition temperatures. Therefore, the cyclic olefin-based polymers are not suitable to uses for which high heat resistance is required. Also, because these polymers have no polar group, they have insufficient bonding and adhesive properties. Particularly, because the polyvinyl alcohol-series polarizer constituting a polarizing plate is hydrophilic, the adhesive property of the polarizing plate to these cyclic olefin-based polymers which are originally hydrophobic is deteriorated significantly as compared with that to triacetylcellulose which is usually used. Moreover, the hydrophilic polyvinyl alcohol-based polarizer itself originally has high hygroscopicity. When the cyclic olefin-based film having a low moisture permeability is used as a protective film constituting the polarizing plate, the water dispersed from the polyvinyl alcohol-based polarizer is prevented from permeation and the inside of the polarizing plate itself is put into a high-temperature and high-moisture state under a high-temperature condition. As a result, fluctuation in light transmittance, the degree of polarization and the like are increased, leading to low reliability. Also, there are problems concerning the production and processing of the polarizing plate that, at the time of producing the polarizing plate using the cyclic olefin-based film having a small moisture permeability as the protective film, the escape of moisture is poor and a long-time drying process is required; and that a long-time humidity conditioning is required when the polarizing plate is used.
The cyclic olefin-based polymers of the above (ii-2) have a high glass transition temperature and are therefore superior in this point. However, the polymers contain no polar group like the polymers of the above (i) and (ii-1) and are therefore inferior in bonding and adhesive properties.
The cyclic olefin-based polymers of the above (ii-3) have a high glass transition temperature and an alkoxycarbonyl group (ester) or an acyloxy group as a polar group, and are therefore superior in bonding and adhesive properties. But they are inferior in anti-hygroscopic properties.
Also, the cellulose triacetate film conventionally used has moisture permeability enough to discharge moisture from a polarizer and, therefore, the permeation of moisture dispersed from a polyvinyl alcohol-based polarizer is not hindered. However, fluctuation in optical performances of the cellulose triacetate film itself as a result of fluctuation in environmental temperature and humidity is found a little.
The cyclic olefin-based polymers of the above (ii-4) have a polar group and are therefore superior in bonding and adhesive properties. However, the polymers have an alkyl group having 3 to 8 carbon atoms and are therefore insufficient for the elastic modulus of a film. Also, there are descriptions as to a hydroxyl group as the polar group in JP-A-2002-20435, however, synthetic examples, action effects on binding and adhesive properties, and production, processing and performance of a polarizing plate are not disclosed or suggested in JP-A-2002-20435.